Incident Energy Dependence Research Articles

Microscopic study of the alpha -16O interaction on the basis of the complex effective interaction and the totally antisymmetrized many-body theory.

The complex internucleus potential for {alpha}-{sup 16}O system is investigated with the microscopic complex effective interaction and the totally antisymmetrized many-body theory. Both real and imaginary parts of the theoretical potential, in which the differences between the oscillator-width parameters of the target and the projectile are taken into account, coincide well with the phenomenological optical potential which is uniquely determined by the experimental results. As for the incident-energy dependence of the real part of internucleus potential, it is found that 70% is caused by the effect of antisymmetrization and that the rest is explained by the energy dependence of the effective interaction. For the imaginary part both the effect of antisymmetrization and the energy dependence of the effective interaction almost equally contribute to the incident-energy dependence.

Sputtering and reflection from lithium, gallium and indium

Computer-simulated data concerning the incident energy and ion temperature dependence of the sputtering yields of lithium, gallium and indium due to light-particle (deuterium and tritium) bombardment are presented together with such data on the selfsputtering yields. Selfsputtering yields against angle of incidence are provided. Particle reflection studies are also included. A figure of merit outlines the applicability of materials in fusion machines.

Continuum protons from 58Ni(p,p') at incident energies between 100 and 200 MeV.

The inclusive reaction $^{58}\mathrm{Ni}$(p,p') was studied at incident energies of 100, 120, 150, 175, and 200 MeV for scattering angles between 15\ifmmode^\circ\else\textdegree\fi{} and 120\ifmmode^\circ\else\textdegree\fi{}. Angular distributions at various emission energies are analyzed in terms of a quasifree knockout reaction mechanism, combined with parametrized systematics which should represent multistep contributions. Reasonable agreement between the experimental data and calculated distributions is obtained, with a consistent incident-energy dependence. The proportion of the quasifree component amounts to \ensuremath{\sim}30% of the preequilibrium yield. The quasifree contribution appears to be in agreement with the first-step yield of the statistical multistep-direct emission theory.

Angular momentum and incident-energy dependence of nucleus-nucleus interaction.

The purpose of this paper is to understand intuitively the origin of the angular momentum and incident-energy dependence of the nucleus-nucleus interaction on the basis of the totally- antisymmetrized many-body theory. With the aim of understanding the structure of the nucleus-nucleus interaction, we show first that the nucleus-nucleus interaction can be written by the use of the density-distribution function and the phase-space distribution function instead of using the many-body wave function itself. And we show that the structure change of the density-distribution function with the increase of the angular momentum causes the angular momentum dependence of the nucleus-nucleus interaction and that the incident-energy dependence of the nucleus-nucleus interaction originates from the structure change of the phase-space distribution function.

Steric effect in the scattering of hexapole-oriented beams of symmetric-top molecules by graphite(0001)

The orientational dependence of the scattering of hexapole-focused, oriented molecule beams of six symmetric-top molecules (CH3Cl, CH3F, CHCl3, CHF3, t-BuCl, CH3CN) and CH3OH from the (0001) surface of a graphite crystal is reported. Experimental angular distribution data are well represented by a two-component model, consisting of a ‘‘trapped/desorbed’’ and a ‘‘direct’’ scattered contribution. The steric effect, defined as the difference (‘‘heads’’ vs ‘‘tails’’) divided by the average of the scattered signals, has been measured as a function of the scattering angle and the degree of orientation of the molecules. There is considerable diversity among the different molecules with respect to the direction and magnitude of the steric effect of the scattering (and trapping). In all cases, however, the magnitude of the steric effect is essentially a linear function of the degree of orientation. Limited data on the incident energy dependence of the angular distributions and the steric effect are also presented. A model which deconvolutes the steric effect for the trapped/desorbed and directly scattered components is introduced. It also provides an independent estimate of the trapping probability of the incident molecules.

Dependence of physical observables on the incident energy in intermediate energy nucleus-nucleus collision.

The experimental results of the dependence of fragment mass yield distribution and related physical observables on the incident energy in intermediate energy nucleus-nucleus collisions reported recently are interpreted with a modified statistical model and relevant averaging techniques. The model reproduces the trends of the variation of mass yield distribution with incident energy quite well. It can also explain the experimental systematics of the incident energy dependence of physical variables with statistical features.

Forward energy flows in nucleus-nucleus collisions and forward nucleon-nucleon collisions at high energies

Connections between forward energy flows in nucleus-nucleus collisions and forward nucleon-nucleon collisions are discussed. It is found that the strong incident energy dependence of the forward energy distributions observed in 16O-nucleus collisions at the CERN SPS is mainly due to kinematics. The correlation between energies in forward and transversal directions is calculated in terms of the multisource model. It is predicted that such a correlation depends also on incident energy.

Step effects in the thermal decomposition of methanol on Pt(111)

Methanol decomposition to adsorbed CO and hydrogen on Pt(111) was observed using time-resolved high resolution electron energy loss spectroscopy. No reaction was seen at temperatures ≲ 180 K, the molecular methanol desorption temperature. Between 180 and 200 K the decomposition reaction is controlled by the small amount of defects present on our carefully prepared sample. This was principally demonstrated by the fact that only 1–2% of a monolayer of CO was formed regardless of the initial methanol coverage. A steady state reaction run between 200 and 240 K showed only a low rate of CO formation (only a few percent of a monolayer even after many langmuir exposure of methanol). At a 300 K surface temperature, decomposition proceeds much faster, with about 10% of a monolayer of CO being formed. The origin of this temperature dependence is attributed to the ability of the product H and CO to diffuse away from sites where they were initially formed. Using a He seeded methanol beam, there was no apparent incident energy dependence for the methanol decomposition reaction.

Asymmetry of spin-flip of polarized protons in the inelastic scattering to the first 2(+) states of 48Ti and 50Ti.

Angular distributions of the differential cross section, analyzing power, spin-flip probability, and spin-flip asymmetry in the excitation of the first ${2}^{+}$ states in $^{48}\mathrm{Ti}$ and $^{50}\mathrm{Ti}$ were measured at incident energies of 11 and 18 MeV using the (p,p'\ensuremath{\gamma}) coincidence technique with a polarized proton beam. The angular distributions show strong incident energy and target dependence. The results were analyzed in terms of a macroscopic coupled-channels method based on the vibrational model and of the microscopic distorted wave Born approximation based on shell-model wave functions and effective nucleon-nucleon interactions. The spin-flip asymmetry is quite sensitive to the spin-dependent part in the interaction that causes inelastic scattering.

Incident energy dependence of preequilibrium (p, p′) spectra

Proton energy spectra from (p, xp) reactions on98Mo and106Pd have been measured at incident energies of 12, 14, and 16 MeV to investigate the incident energy dependence of preequilibrium (p, p′) process. The (p, xp) energy spectrum for60Ni has also been measured at an incident energy of 18 MeV to confirm the mass number dependence. These spectra were compared with a calculation based on the exciton model in which the square of the average effective matrix element ¦M¦2 was assumed to beKA−3E−1 and isospin conservation was taken into account. The calculated spectra using a constantK-value (430 MeV3) were in good agreement with all the measured ones. The role of isospin conservation in preequilibrium process was discussed through the present analyses.

Various Effects on the Nonrelativistic DWIA for (p, 2p) Reactions

We study various effects on both the analyzing powers and the cross sections for the (p,2p) reactions. Numerical calculations with the nonrelativistic distorted wave impulse approximation are carried out for the cross sections and the analyzing powers for the 40Ca(p, 2p)39K reaction at 101.3, 200 and 300 MeV using the effective nucleon· nucleon interaction. We take into account both the effect of the spin·orbit interaction for the distorted waves and the off-shell effect of the proton-proton scattering. It is found that the data for 101.3 and 200 MeV are in good agreement with our calcula'tions. However, in the case of 300 MeV, significant discrepancies between the experimental results and the calculated ones have been shown. We study the sensitivity to the choices of distortion parameters of the optical potentials. Also, for the first time we examine nonlocality effects for both the distorted wave functions and the bound state ones. Finally we study the effects of relativistic corrections in the distorted wave functions and factorization corrections. The incident energy dependence of the various corrections to the cross section and the analyzing power was found not to be so large. Although the inclusion of the various corrections has some effects upon the NR-DWIA calculations, it does not significantly affect the quality of the agreement with the data of 300 MeV.

Intermediate mass fragment production mechanism in relativistic 4He+Au interactions

The cascade-percolation model is proposed to interpret the experimentally observed incident energy dependence of mass yield slopes for intermediate mass fragments generated in inclusive relativistic 4He+Au reactions. A mass moment correlation analysis is performed for the more sophisticated exclusive data.

Electron-irradiation-induced crystalline to amorphous transition in α-Sic single crystals

Abstract An electron-irradiation induced crystalline-to-amorphous (C-A) transition in α-Sic single crystals of the 6H polytype has been studied as a function of irradiation temperature, incident electron energy and orientation of the incident beam, by means of ultra-high voltage electron microscopy. The C-A transition can be induced at temperatures below 290 K. The minimum energy of incident electrons to cause the C-A transition is 725 ± 25 keV. The electron dosage required for the C-A transition is essentially constant at temperatures below 220 K, while at temperatures above 220 K, the dosage increases quickly with temperature until no amorphization can be induced any more at the critical temperature of 290 K. At fixed temperatures below the critical temperature, the required dosage decreases with increasing incident electron energy. The temperature and incident energy dependence of the required dosage indicate that a knock-on mechanism rather than an ionization mechanism is responsible for the C-A transition. The amorphization dosage of the irradiation along the ⟨1120⟩ and ⟨1100⟩ directions (i.e. parallel to the basal plane) is smaller than that of the irradiation along the ⟨0001⟩ direction (i.e. perpendicular to the basal plane). The crystallization temperature of the irradiation-produced amorphous Sic is 1148 ± 25 K.

Reflection electron-energy-loss spectroscopy, x-ray-absorption spectroscopy, and x-ray photoelectron spectroscopy studies of a new type of layer compound CrPS4.

A new type of layer compound, ${\mathrm{CrPS}}_{4}$, has been investigated by means of reflection electron-energy-loss spectroscopy (REELS), x-ray-absorption spectroscopy (XAS), and x-ray photoelectron spectroscopy (XPS). Information on the bonding states of the compositional atoms and the occupied energy states has been deduced from the core- and valence-electron XPS results. The binding energies and the multiplet structures of core levels have been discussed in detail. Information on the unoccupied energy states has been deduced from the XAS results. On the basis of the REELS results, energy positions and the joint density of states have been discussed. The optical properties have been investigated through the Kramers-Kronig analysis of the REELS spectrum. We have made an attempt to derive the depth profile of the localized energy states from the incident-energy dependence. A schematic energy-band model has been proposed.

Neutralization of noble-gas ions at very low energies.

Neutralization of noble-gas ions (${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$) on Pt(100) has been studied. It is common to the three kinds of projectiles that the ion yield shows a V-shaped incident-energy dependence at very low energies. The minimum position of the yield and the steepness of the V shape depend on the projectile ion species. The ion-yield change is governed by the change of the ion survival probability against Auger neutralization. Angular distributions show that the ion yield becomes higher in small-angle scattering with decreasing incident energy. A new empirical model is presented for the ion survival probability depending on penetration depth and residence time in the ion-surface interaction region.

Activated dissociative adsorption of N 2+ on Ni(100) and Ni(111)

We have studied the adsorption of atomic nitrogen on Ni(100) and Ni(111) upon exposure to very low energy (1–20 eV) N 2 + and N + ion beams. The amount of adsorbed N was measured by Auger electron spectroscopy. The adsorption rate for N + is nearly constant as a function of the incident energy, while the dissociative adsorption rate for N 2 + shows a strong incident energy dependence and a resonance-like feature is observed at incident energies of 2–3 eV on Ni(100) and ~ 4 eV on Ni(111). The results for N 2 + can be explained by two channels: one is from electronically excited molecules, N 2 ∗, generated by resonance neutralization, and the other is from the ground state N 2. The resonance-like feature, which is structure-sensitive, can be explained by the deexcitation of N 2 ∗ correlated to the N-adsorbed structure on Ni(100) and Ni(111).

Breakdown of Dipole Selection Rules in Electron-Excited 3p-3d Transitions within Localized Transition-Metal Ions at Low Incident Energies

Metal M 2,3 inner-shell electron-energy-loss spectra in layered transition-metal tri-thiophosphates MPS 3 (M=Mn, Fe, Ni) have been measured at low incident energies in reflection geometry. The spectra reveal the multiplet structures of the final states of localized divalent metal ions. The relative intensities of the peaks are varied systematically as incident energy decreases. Large deviation from the X-ray absorption spectra are found at low incident energies. The variations are interpreted in terms of the incident energy dependence of momentum transfer involved in the inelastic scat-tering process and exchange interaction between incident and target electrons. It is found that dipole selection rules are broken in 3p-3d transitions within the localized 3d transition-metal ions as incident energy approaches the excitation threshold.

Proton-induced spallation reactions between 300 MeV and 20 GeV.

Proton-induced spallation reactions are studied in the energy region from 300 MeV to 20 GeV. An analytical expression is derived for the production cross sections of target residues in which the incident proton energy dependence of the cross sections is described by variation of a single parameter. Rather good agreement is obtained with experiment when reasonable physical assumptions for the variation of this parameter are made.

Dissociative chemisorption of H2 on Ni surfaces: Incident kinetic energy dependence and the characteristics of the potential energy surface

This paper demonstrates that the dependence of the dissociative sticking probability on incident kinetic energy can be changed significantly without materially changing the activation barrier. The presence of a potential well in the entrance channel and the detailed curvature of the potential energy surface also influence this dependence.

Backward production of protons in proton-nucleus collisions at low and intermediate energy.

We study inclusive cross sections for backscattered protons in proton-nucleus collisions at the incident energies of 35--300 MeV. We evaluate the contributions from the two-nucleon cluster reaction as well as from the single scattering mechanism. Realistic Fermi momentum distributions are considered for both reaction mechanisms. It is found that, at 300 MeV, the two-nucleon cluster reaction dominates the inclusive cross section while, below 200 MeV, the two processes are in competition with each other and depend on the observed energy of the backscattered proton. We present the incident energy dependences of the cross sections at fixed energies of the backscattered protons to clarify the reaction mechanisms.